DESCRIPTION: The proposal aims to clarify the role of insulin and race on cardiovascular reactivity. It hypothesizes that blacks and patients with increased insulin will have increased cardiovascular plasma norepinephrine and epinephrine, neuropeptide-Y, renin, total peripheral resistance, and cardiac output. Eighty black and white normotensive and hypertensive individuals will be studied. They will then be admitted twice to the Clinical Research Center. One 4-day admission will provide a high carbohydrate diet which will stimulate insulin production; the other 4-day admission will provide a low carbohydrate diet and minimal insulin stimulation. Sequence of diet will be randomized, and sodium excretion will be measured throughout each admission. Insulin levels will be defined with a two hour glucose tolerance test. Alpha and beta adrenergic receptors will be measured in lymphocytes and platelets. Beta-receptor end organ sensitivity will be measured with isoproterenol infusions. Baroreceptor functioning will be characterized with phenylephrine infusions. Each person will be characterized at rest in terms of blood pressure, heart rate, total peripheral resistance, stroke volume, plasma catecholamines, atrial natriuretic factor, neuropeptide-Y, and chromogranin-A. Similar variables will be studied while the individual performs mildly stressful tasks.